Failure of an energy storage device, such as a rechargeable battery or battery cell, can result from, for example, stress events. Stress events can include, for example, charging at a sub-freezing temperature, vibrations, or a collision. Energy storage device failures can result in, for example, a mild short or thermal runaway. A mild short can cause elevated self-discharge where heat buildup is minimal because power discharge is low. However, if enough metallic particles converge in one spot, a sizable current can begin to flow between electrodes of a cell, and the spot can heat up and weaken. Thermal runway can result in a battery cell temperature quickly reaching 500° C. (932° F.), at which point the cell can catch fire or explode. Thermal runaway is also known as “venting with flame” and “rapid disassembly” by some industry professionals.
Battery cells in a battery module, such as may be used in an electric vehicle, are typically in close proximity to one another. An explosion of one cell in a battery module can propagate to other cells in the battery module, causing the other cells to become thermally unstable or explode. An explosion can propagate to multiple cells or an entire battery pack in a chain reaction, resulting in catastrophic damage to the battery module and anything within proximity of the battery module.
Additionally, accidental collision is possible even in the most conservative and advanced electric vehicles, putting the electric vehicles and occupants at risk from fire or explosion of an energy storage device due to a collision. The energy density of battery cells is expected to double every few years, with 10 times current energy density being developed in university laboratories. The higher the energy density of an energy storage device is, the more critical safety features become for both vehicle safety and longevity of energy storage devices.